Brief objectives: To identify the carcinogenic substances in betel nut and in unburned chewing tobacco. Approach: Standard chemical procedures will be utilized to separate the active agents from these substances. The relative carcinogenic activity of the various fractions will be assessed by their ability to produce epithelial tumors after topical applications to the mucosa of the hamster buccal pouch. Carcinogenicity of the fractions will also be assessed by their ability to produce tumors after injection into grafts of fetal oral tissue implanted into isologous hamster buccal pouch mucosa. Recent progress: Crude dimethyl sulfoxide extracts of betel nut produce tumors after 18 weeks of topical application (3X/wk). Latent period and susceptibility to tumor development are shortened if male hamsters are injected with estrogenic hormones. Injections of extract or implantation of gelatin pellets (containing betel nut extract) directly into buccal mucosal grafts of fetal hamster oral tissue result in epithelial tumor development within 15 weeks. Similar experiments are in progress to identify carcinogens in unburned tobacco.